As digital television technology becomes more readily available to an increasing number of consumers, many cable operators have made efforts to offer programming content formatted according to digital television standards. However, these cable operators face a mixture of competing demands—while an increasing number of users have televisions capable of displaying pictures based on high definition television (HDTV) standards, other users have televisions that display pictures based on the older, standard definition television (SDTV) standard.
The standards developed by the Advanced Television Systems Committee (ATSC), which include digital HDTV and SDTV, specify technologies for the transport, format, compression, and transmission of digital television in the United States. HDTV provides a very high quality display, with a vertical resolution display from 720p to 1080i and higher, and an aspect ratio (the width to height ratio of the screen) of 16:9. For example, one common HDTV format specifies a display having 1920×1080 pixels. SDTV has a range of lower resolutions and commonly provides a 4:3 aspect ratio. For example, one common SDTV format specifies a display having 640×480 pixels. The ratios “4:3” and 16:9” are used herein as adjectives to describe an image, such as an icon, a video frame, or a group of pixels, that is formatted for a respective aspect ratio. For example, an icon defined for a 4:3 aspect ratio is referred to as a “4:3 icon.”
In a typical cable television network, a digital television signal transmitted from a cable operator's headend is received and processed at a user's home by a set-top terminal. A set-top terminal receives, from the cable network, encoded signals containing programming content and other data, decodes the signals, and converts them into signals displayable by the television. A set-top terminal also accepts commands from the user relating to the user's choices for programming and services.
Several techniques exist for displaying a 4:3 image on an HDTV display. One common reformatting technique defines a 4:3 frame in the middle of the television screen, leaving bars of unused space on both sides. The resulting display is unsatisfactory from a technical standpoint because it does not fully utilize the television screen. Additionally, some viewers find the appearance of the bars on the screen to be aesthetically displeasing.
A second approach applies image processing techniques to “stretch” a 4:3 image to create a 16:9 image. This may be achieved, for example, by upsampling the 4:3 image data. The resulting image fills the television screen; however, the “stretched” image may appear distorted. Because each pixel in the 4:3 image is defined to appear square when displayed on a 4:3 screen, “stretching” such a pixel for a 16:9 screen causes the pixel to appear rectangular or another shape. As a result, the reformatted image as a whole may appear distorted. For example, circular objects may appear elliptical in the 16:9 image.
A third approach used by some cable operators is to broadcast two versions of a given program to set-top terminals in the cable network. According to this method, a first signal is formatted for a 4:3 display and is transmitted via a carrier on a first transmission channel; a second signal is formatted for a 16:9 display and is transmitted via a carrier on a second transmission channel. Some existing set-top terminals have the capability to determine the aspect ratio of a television set and, in response, tune to the appropriate transmission channel to receive the signal, corresponding to the display characteristics of the television. This technique has the disadvantage of doubling the required amount of transmission bandwidth.
The conflicting HDTV and SDTV formats affect not only the programming content offered by cable operators, but also any other material of a graphical nature that is provided to users. For example, in addition to programming content, many cable operators provide program guide data to the set-top terminals in the network from time to time. Program guide data may be used, for example, in an interactive program guide (“IPG”) application to provide to users information concerning available programs. Program guide data typically contains time and channel information concerning each program to be broadcast within a predetermined period. After receiving the program guide data from the cable network, a set-top terminal stores it in memory. This stored data is updated from time to time to provide the latest program guide information.
In addition to time and channel information, program guide data often includes data pertaining to one or more graphical images such as video clips, individual video frames, icons, etc. Such graphical images may be used, for example, in a graphical user interface for presenting the time and channel information to the user. A data file, or a set of data files, within the program guide data that represents a single graphical image or a set of related graphical images is referred to as a “graphical component.” Thus, a graphical component may comprise, for example, data representing a single video frame, a series of video frames, or an icon.